Normally dormant supermassive black holes do not give off any light or radiation as they are not actively devouring matter. They can only be indirectly observed by the pattern of stars around them.
But astronomers at the University of Maryland and the University of Michigan were able to observe x-rays bouncing around a disk of debris around a supermassive black hole called Swift J1644+57.
Sitting in the centre of a small galaxy in the Draco constellation about 3.8 billion light years away, the giant black hole appears to have woken from its slumber to destroy the star.
What remains of stars devoured by the black hole sit around it in a puffy cloud known as an accretion disk.
The X-rays given off by the star as it was torn apart have helped to illuminate this disk.
Dr. Erin Kara, an astronomer at the University of Maryland who was the lead author of the study, said: “Before this result, there was no clear evidence that we were seeing into the innermost regions of the accretion disk.”
“We thought the emission was from the jet pointed at us, or further away and not close to central black hole.”
“This new study shows us that, actually, we can see this reverberation at work very close to the central black hole.”
The feeding frenzy that occurs when a star strays too close to a dormant star is known as a tidal disruption event. Occassionally these light up with x-rays.
The disk of debris acts like a reflective shield behind a flashlight bulb, reflecting and focusing the radiation given off.
Dr Kara said: “Most tidal disruption events don’t emit much in the high-energy X-ray band.”
“But there have been at least three known events that have, and this is the first and only such event that has been caught at its peak.”
Conventional wisdom among astronomers has long held that, during a tidal disruption event, high-energy X-rays are created further from the black hole in the relativistic jets – huge beams of particles ejected by the black hole and accelerated to nearly the speed of light.
But seeing X-ray emissions bouncing off the walls of the inner accretion disk has cast a new light on this assumption.
The team used X-ray reverberation mapping to chart out the inside of the accretion disk, much in the same way that sound waves can be used to map the seafloor or canyons by measuring the time delays of echoes.
The researchers, whose work is published in the journal Nature, computed small delays in the arrival time of X-ray signals reflected from iron atoms in the accretion disk.
Dr. Kara said: “We know how sound echoes in a large auditorium, for example. Because we know the speed of sound, we can use the time delay information to calculate the shape of the auditorium.”
“We are doing the same with X-ray radiation to map out the inner accretion disk. It’s a cool, novel technique that has only been developed within the last six years.”
To date, most of what astronomers know about supermassive black holes comes from a handful of black holes that are actively gathering and consuming matter.
It is thought, however, that these account for just 10 per cent of the supermassive black holes in the universe.
Please like, share and tweet this article.
Pass it on: New Scientist